Turbocharged engines utilize a turbocharger to compress intake air and increase the power output of the engine. A turbocharger may use an exhaust-driven turbine to drive a compressor which compresses intake air. As the speed of the compressor increases, increased boost is provided to the engine. Upon receiving an increased torque demand, it may take an amount of time for the turbine and compressor to speed up and provide the required boost. This delay in turbocharger response, termed turbo lag, may result in a delay in providing the demanded engine power. The volume of the induction system of the engine may also delay the time to pressurize that volume of air. As such, turbo lag and increased induction system volume may result in engine torque response delays.
Other attempts to address turbo lag and engine torque response delays include including an electric assist compressor on the primary induction passage. While the electric compressor may provide extra boost, the electric compressor still has to pressurize the entire induction system volume of air, thereby delaying torque response. Another method to reduce engine torque response delays includes utilizing a dual turbocharger arrangement in which two turbochargers are arranged in parallel or in series along the induction path. While the addition of a second turbocharger may reduce turbo lag, this may also increase the size and cost of the engine system.
In one example, the issues described above may be addressed by a method for controlling intake airflow through two parallel induction flow passages of an engine. A first flow passage may include a turbine-driven compressor and a second flow passage may include an electric compressor. Upon receiving an increased torque request, the electric compressor on the second flow passage may provide increased boost to an intake manifold of the engine.
In one example, in response to a driver tip-in, a throttle in a first induction flow passage, downstream of an exhaust-driven turbocharger compressor, may be temporarily opened. At the same time, an electric compressor may be driven to also drive flow into an intake manifold through a second induction flow passage, in parallel with the first induction flow passage. Specifically, the throttle may be fully opened and the electric compressor may be turned on in response to the tip-in, or increased torque demand. Once manifold pressure increases to atmospheric pressure, the throttle may be closed while continuing driving of the electric compressor to provide boosted air to the intake manifold. During this time, the turbine-driven compressor may increase speed, thereby increasing boost pressure in the first induction passage. In response to boost pressure increasing above the manifold pressure, the throttle may open to provide the required boost. In this way, turbo lag may be reduced, thereby decreasing the delay in engine torque response.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.